1. Field of the Invention
The present invention relates to an automatic stop and restart device for an engine, which stops an engine automatically when a predetermined automatic engine stop condition is satisfied and restarts the engine when a predetermined restart condition is satisfied after the automatic engine stop condition is satisfied.
2. Description of the Related Art
In recent years, there are developed automatic engine stop and restart systems which stop an engine automatically and then restart the engine automatically for a purpose of improving fuel efficiency of automobiles or decreasing environmental load. The automatic engine stop and restart system automatically stops the engine if a predetermined automatic engine stop condition for stopping the engine is satisfied by a driver's operation (e.g., if a brake operation is performed at vehicle speed under a predetermined speed). In addition, the automatic engine stop and restart system automatically restarts the engine if a predetermined restart condition is satisfied by a driver's operation (e.g., if a brake releasing operation or a gas pedal depressing operation is performed).
For instance, Japanese Patent No. 4214401 discloses a conventional device in which, if a request for restart is issued during a period of decreasing engine rotation just after idle stop, a controller starts a cranking operation without waiting for the engine rotation being completely stopped. More specifically, in this conventional device, if a request for restart is issued during a period of decreasing engine rotation just after idle stop, the controller controls a starter pinion gear to rotate. Further, when the rotation speed of the starter pinion gear is synchronized with a predicted rotation speed of a ring gear, the controller controls the starter pinion gear to engage with the ring gear so as to start the cranking operation.
Next, operation timings of the conventional device as disclosed in Japanese Patent No. 4214401 are described with reference to a timing chart illustrated in FIG. 31. In FIG. 31, a ring gear rotation speed is represented by reference numeral 1001; a pinion gear rotation speed, 1002; a starter drive signal, 1003; and a pinion gear thrust signal, 1004. An automatic engine stop condition is satisfied at time t1, and the controller starts the engine stop process. After that, an engine restart condition is satisfied at time t2, and the controller turns on the starter drive signal so that the pinion gear starts to rotate.
Further, at time t3, it is predicted that the ring gear rotation speed and the pinion gear rotation speed are synchronized with each other after a pinion gear abutment delay time ΔT. Therefore, the controller turns on the pinion gear thrust signal. At time t4, the ring gear rotation speed and the pinion gear rotation speed are synchronized with each other. At the same time, the pinion gear abuts against and engages with the ring gear. After that, the controller controls the pinion gear to rotate and drives the ring gear so that the engine is cranked and is restarted.
In the conventional device as disclosed in Japanese Patent No. 4214401, the controller predicts the ring gear rotation speed in the future and controls timing to thrust the pinion gear in synchronization with the timing when it is predicted that the pinion gear rotation speed and the ring gear rotation speed are synchronized with each other. However, the conventional device as disclosed in Japanese Patent No. 4214401 considers nothing about the case where the driver selects the non-drive range during the engine restart process.
Therefore, in this case, a ring gear rotation speed decrease amount in the non-drive range is different from a ring gear rotation speed decrease amount in the drive range. Therefore, the pinion gear rotation speed and the ring gear rotation speed cannot be synchronized at a time point of abutment, and the pinion gear is pressed to the ring gear in the state where the gears cannot engage with each other. As a result, in the conventional device as disclosed in Japanese Patent No. 4214401, there is a risk that noise is generated or a mechanism is broken.
The above-mentioned problem of the conventional device as disclosed in Japanese Patent No. 4214401 is described with reference to a timing chart illustrated in FIG. 32. In FIG. 32, the ring gear rotation speed is represented by reference numeral 1001; the pinion gear rotation speed, 1002; the starter drive signal, 1003; the pinion gear thrust signal, 1004; and a transmission state, 1005. At a time point t1, the automatic engine stop condition is satisfied, and the controller starts the engine stop process.
After that, at a time point t2, the engine restart condition is satisfied. Therefore, the controller turns on the starter drive signal so as to control the pinion gear to start rotating. Then, at a time point t3, the controller predicts that the ring gear rotation speed and the pinion gear rotation speed are synchronized with each other after the pinion gear abutment delay time ΔT and turns on the pinion gear thrust signal.
At a time point t4, the transmission state is changed from a D range to an N range, and hence the ring gear rotation speed decrease amount changes. As a result, at a time point t5, the ring gear and the pinion gear abut against each other but cannot engage with each other because the ring gear rotation speed and the pinion gear rotation speed are not synchronized with each other. Therefore, noise may be generated or the mechanism may be broken.